Minute amount (similar to 1 ppm) of acrylonitrile (AcN), a possible contaminant, shows an unexpected enhancement for the direct electro-oxidation of formic acid (FAO) at Pt nanoparticles modified GC (nanoPt/GC) electrodes. This is reflected by a remarkable increase of the current intensity of the direct oxidation peak (I-p(d), at ca. 0.3 V) in the presence of AcN, concurrently with a significant decrease of the second (indirect) oxidation current (I-p(ind), at ca. 0.7 V), compared to that observed in the absence of AcN (i.e., at the unpoisoned Pt electrode). The extent of enhancement depends on the surface coverage (theta) of AcN at the surface of Pt nanoparticles. AcN is thought to favor the direct FAO by disturbing the contiguity of the Pt sites, which is necessary for CO adsorption. Furthermore, XPS measurements revealed a change in the electronic structure of Pt in presence of AcN, which has a favorable positive impact on the charge transfer during the direct FAO. (C) 2014 Elsevier B.V. All rights reserved.